In this study, we describe a multi-wavelength laser at wavelengths of 634, 644, and 655 nm based on cascaded nonlinear frequency conversion. The cascaded frequency conversion process is jointly performed using the KTiOPO4 (KTP) and KTiOAsO4 (KTA) crystals. First, optical parametric oscillation is conducted in an x-cut KTP crystal to convert the 1064-nm laser into a 1572-nm laser. Sum frequency generation is subsequently achieved in a (θ=90° and φ=20.9°)-cut KTA crystal for the sum frequency mixing of 1064 and 1572 nm, generating a 634-nm laser output. Raman frequency conversion is further utilized in the x-cut KTP crystal to convert the 634-nm laser into first-order Raman radiation at 644 nm and second-order Raman radiation at 655 nm, simultaneously achieving multi-wavelength emissions at 634, 644, and 655 nm. The cascaded frequency multi-wavelength laser has a maximum average output power of 1.7 W, a pulse width of 19.3 ns, and a repetition rate of 6 kHz.